F.2 Supervisory tones

22.0013GPPPrinciples of circuit telecommunication services supported by a Public Land Mobile Network (PLMN)Release 17TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

F.2.1 General

Supervisory Tones, indicating primarily ringing, engaged and unobtainable numbers, may be generated by both the PLMN and PSTN.

Except for ring tone, all tones indicating call progress to a user shall be generated in the UE, on the basis of signals from the network where available, and are according to the standard defined in the present document.

Tones sent to a caller to a UE will be generated in the network, generally local to the caller, and will be to the standard of his local exchange, except for mobile to mobile calls, where the tones will be generated in the calling UE. For mobile terminated calls, the ring tone will be generated in the called MSC (except OACSU).

F.2.2 Method

In the interests of early release of the traffic channel on failure to succeed in setting up a (mobile originated) call, where possible supervisory tones should be indicated over signalling channels. The UE will then generate the required tones. However, if the network generates an in-band announcement this will be indicated to the UE. In this case the UE shall connect the user to the announcement until instructed to release the call, either by the user or by the network. An alternate procedure may apply for UE able to generate appropriate announcements internally.

The ring tone will be sent over the traffic channel, since this channel must be available for traffic immediately it is answered (exception: Off Air Call Set Up). The Ring Tone is therefore generated by the PLMN or PSTN supporting the called phone.

On failed mobile terminated call attempts, the called MSC will either signal to the caller, if this is possible, or else will generate the required supervisory tones.

"Alert" is not a supervisory tone. The indication is signalled, and the UE may generate any form of indication to the user that the UE is being called.

F.2.3 Standard tones

UE generated tones will be generally in accordance with CEPT, ANSI T1.607, or Japan recommendations, where appropriate, and are listed in table 1. Any network originated tones will be according to PLMN or PSTN choice.

F.2.4 Applicability

This method will apply in all cases where signalling is capable of indicating the supervisory tone required. However, for connection to certain fixed networks where this signalling is not possible, fixed network tones will be carried over the traffic channel.

User equipment may employ any suitable technique to indicate supervisory information. However, if tones are employed, they shall be in accordance with the present document. The use of these tones in the MSC is preferred.

NOTE 1: The tones and/or announcement to the calling party should not be provided if the Information transfer capability is set to UDI.

NOTE 2: For a call with information transfer capability set to 3.1 kHz, the use of tones and/or announcement may cause the expiry of an awaiting answer timer in a modem or fax machine.

F.2.5 Comfort tones

If desired by the PLMN operator, the network may optionally introduce "comfort tones" while the call is being connected, during what would otherwise be silence. This would be overridden by indication of a supervisory tone, an announcement or by traffic. PLMNs may offer this feature optionally to incoming or outgoing callers.

The "comfort tones" may take the form of tones, clicks, noise, music or any other suitable form, provided that they cannot be confused with other indications that might be expected.

This feature is intended to indicate to the user that his call is progressing, to prevent him terminating the call prematurely.

Table 1: Supervisory tones in UEs

Tone

Frequency

Tolerance

Type

CEPT

ANSI

Japan

CEPT ANSI

Japan

CEPT

ANSI

Japan

Dial tone (optional)

425 Hz

350 Hz added to 440 Hz

400 Hz

15 Hz

20Hz

Conti-nuous

Continuous

Conti-nuous

2 *

Subscriber Busy (Called Number)

425 Hz

480 Hz added to 620 Hz

400 Hz

15 Hz

20Hz

Tone on 500ms
Silence 500ms

Tone on 500ms Silence 500ms

3 *

Congestion

425 Hz

480 Hz added to 620 Hz

Optional

15 Hz

Optional

Tone on 200ms
Silence 200ms

Tone on 250ms
Silence 250ms

Optional

Radio Path
Acknowledgement (Mobile
Originated only) (optional)

425 Hz

400 Hz

15 Hz

20 Hz

Single tone 200ms

Tone on 1 Sec Silence 2 Sec

{Radio Path Not Available
{Call Dropped – Mobile originated only

425 Hz

Optional

15 Hz

Optional

200ms} On/off 200ms} for 3
burst

200ms} On/off 200ms} for 3 burst

Optional

6 *

Error/Special Information}

Number Unobtainable }

Authentication Failure }

950 Hz

1400 Hz

1800 Hz

950 Hz

1400 Hz

1800 Hz

Optional

50 Hz

Optional

{Triple Tone

{Tones on 330ms

{Silence 1.0s

Triple Tone

{Tones on 330ms

{Silence 1.0s

Optional

Call Waiting Tone (CEPT)

425 Hz (tolerance 15 Hz), on for 200 ms, off for 600 ms on for 200 ms, off for 3 s, on for 200 ms, off for 600 ms on for 200 ms. This tone is superimposed on the audio traffic received by the called user. Alternate tones are acceptable but not preferred.

Call Waiting Tone (ANSI)

440 Hz, on for 300 ms, 9,7 s off followed by (440 Hz, on for 100 ms off for 100 ms, on for 100 ms, 9,7s off and repeated as necessary) This tone is superimposed on the audio traffic received by the called user.

Call Waiting Tone (Japan)

Optional

Definition of these and other tones, together with advice on announcements, may be found in CEPT T/CS 20-15 and in T/SF 23.

NOTE: *: The duration of these tones is an implementation option. However, in each case, the UE should be returned immediately to the idle state, and will be able to originate/receive calls, which will override these tones.

Ringing Tone (Alternative

National options permitted)

425Hz

440 Hz added to 480 Hz

Optional

15 Hz

Optional

Tone on 1 s Silence 4 s

Tone on 2 s Silence 4 s

Optional

For application of Call Control Cause Information Elements to these tones, see F.4.